POS0243 KYNURENINE METABOLITES LIMIT INFLAMMATION THROUGH TRICARBOXYLIC ACID CYCLE (TCA) REMODELING
Authors: J. Jäger, C. Makowiec, M. Yang, S. J. Camerin, U. Duthaler, R. Ivanek, Y. Schlup, A. Sokol, G. Bantug, D. Kyburz, C. Hess, C. Frezza, B. Müller
Journal: Annals of the Rheumatic Diseases (2023)

<h3>Background</h3> Following LPS stimulation, extensive transcriptional and metabolic reprogramming leads to metabolic remodeling that allows macrophages to dynamically adopt to environmental cues.<sup>[1]</sup> A failure to accurately orchestrate macrophage responses can skew immune responses towards inflammation and various disease states.<sup>[2]</sup> <h3>Objectives</h3> Macrophages have a central role in Rheumatoid arthritis (RA) by promoting chronic inflammation and joint destruction. Although targeted biologicals have transformed treatment options for RA patients, almost half of them fail to achieve clinical remission<sup>[2]</sup>. Better understanding of the regulation of key immuno-metabolic pathways in macrophages of RA patients will inform on how cellular metabolism and inflammation interlink to identify novel metabolism-related therapeutic targets. <h3>Methods</h3> To delineate disease-specific effects in monocytes and macrophages derived from RA patients compared to healthy individuals we performed whole transcriptome analysis (RNA-Sequencing) and untargeted metabolomics. By integrating these datasets with metabolite assessment in the serum of RA patients, we found upregulation of Indoleamine 2, 3-dioxygenase 1 (IDO1) and cumulation of L-kynurenine (KYN) to be hindered in peripheral blood monocytes and macrophages derived from rheumatoid arthritis (RA) patients compared to healthy individuals in response to LPS. <h3>Results</h3> In macrophages, we identified cumulation of KYN in response to LPS, to limit pro-inflammatory macrophage functions through tricarboxylic acid (TCA) cycle remodeling, characterized by decreased succinate-dehydrogenase (SDH) activity and increased Gluthathione synthesis. Aligning with these findings, kynurenine exerted anti-inflammatory effects when administrated to LPS-activated macrophages in vitro by limiting the production of Interferon gamma (IFNγ) and Tumor Necrosis Factor (TNF). Using the small molecule IDO1 inhibitor Linrodostat and exogenously added KYN we showed that KYN accumulation in response to LPS regulates the glycolytic switch and cumulation of metabolites associated with inflammation such as glycolytic intermediates and the TCA cycle intermediates Succinate and Itaconate. <h3>Conclusion</h3> Collectively, our data highlight KYN as a key immunometabolite that directly interferes with macrophage activation and suggest that dysregulation of the kynurenine pathway in RA patients mediates inflammation and disease progression. <h3>References</h3> [1]Mosser, D.M., Hamidzadeh, K. &amp; Goncalves, R. Macrophages and the maintenance of homeostasis. <i>Cell Mol Immunol</i><b>18</b>, 579-587 (2021). [2]Humby, F. <i>et al.</i> Rituximab versus tocilizumab in anti-TNF inadequate responder patients with rheumatoid arthritis (R4RA): 16-week outcomes of a stratified, biopsy-driven, multicentre, open-label, phase 4 randomised controlled trial. <i>Lancet</i><b>397</b>, 305-317 (2021). <h3>Acknowledgements</h3> We thank the CECAD Research center and especially Christian Frezza and Ming Yang for performing mass spectrometry analyses of samples. We thank the Blood Donor's Center of the University Hospital of Basel and the Department of Rheumatology. <h3>Disclosure of Interests</h3> None Declared.